A variety of cells present in the nerve system form a nerve network that supports high-level brain functions. Elucidation of mechanisms of differentiation, development and apoptosis of the nerve system is an important research subject, to deepen our understanding of functions of nerve system or critical mechanisms of nerve-related disorders. Thus, researches in this field have been energetically pursued.
Recently, a number of novel signal transducer molecules, including the PDZ protein, have been discovered one after another, as indicated by reports on the complex formation of receptors or ion channel molecules with the PDZ proteins such as PSD95/SAP90 in the post-synapse density (PSD) of postsynaptic membrane to perform the signal transduction (Science 269, 1737-1740 (1995), Nature 378, 85-88 (1995), Neuron 17, 103-113 (1996), Neuron 17, 255-265 (1996), J. Neurosci. 16, 2157-2163 (1996), Nature 386, 223, 239 (1997), TIBS 21, 455-458 (1996), J. Yanagisawa et al. (1997) J. Biol. Chem. 272, 7167-7172).
PDZ proteins are thought to serve as modular proteins in the formation of a protein complex, which transmits signals from outside to inside of cells and is as compact as possible. Thus, such proteins play an important role in the complex signal transduction of the nerve system.
On the other hand, glycoproteins present on the cell membrane are expected to function as the receptor to receive such external signals. Thus, there has been a high demand for the isolation and analysis of these membrane proteins for elucidating signal transduction mechanisms in the brain.